1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to cradle stop assemblies for electrical switching apparatus, such as circuit breakers. The invention also relates to operating mechanisms for electrical switching apparatus. The invention further relates to electrical switching apparatus employing cradle stop assemblies.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, and other fault conditions.
As shown in FIG. 1, circuit breakers such as 2 typically include a housing 4, separable electrical contacts 6,8 enclosed by the housing 4, and a spring powered operating mechanism 10 which opens the electrical contacts to interrupt the current through the conductors of an electrical system in response to electrical fault conditions. The electrical contacts 6,8 generally comprise one or more movable contacts 6 and one or more corresponding stationary contacts 8. Each movable contact 6 is disposed at or about a first end 12 of a spring-biased movable contact aim 14. The spring-biased movable contact arm 14 is pivotably coupled, at or about its second end 16, to a crossbar 18 of the operating mechanism 10. The crossbar 18 carries the movable contact arms 14 for all of the poles 20 (one pole 20 is shown) of the circuit breaker 2, and cooperates with a cradle 22 of the circuit breaker operating mechanism 10 to allow for simultaneous opening and closing of the contacts 6,8 in all of the poles 20.
The operating mechanism 10 controls the spring-biased movable contact arm 14 to pivot the movable contact 6 into and out of electrical contact with the corresponding stationary contact 8. A contact arm spring 24 biases the second end 16 of the movable contact arm 14, proximate the operating mechanism crossbar 18, in order to maintain the closed position (shown in phantom line drawing) of the pair of movable and stationary contacts 6,8. A cradle stop pin 26 stops cradle 22 at the desired position and prevents it from undesirably over-rotating (e.g., in the counterclockwise direction, from the perspective of FIG. 1) and, for example, interfering with the movable contact arm 14.
The cradle stop pin 26 suffers from a unique set of disadvantages. Among them, is the fact that the movable contact arm 14 of the circuit breaker contact assembly sometimes strikes the pin 26 during operation (e.g., when the circuit breaker is turned OFF; when the circuit breaker trips open) of the circuit breaker 2, which can cause one or both of the contact arm 14 and the pin 26 to bend and/or break. Also, the movable contact arm 14 sometimes undesirably arcs with the cradle stop pin 26 during interruption, thereby causing poor circuit breaker performance and/or failure to clear the electrical fault.
In an attempt to overcome the foregoing disadvantages, one prior proposal has been to notch the cradle stop pin with a cut-out which is structured to provide clearance for the movable contact arm of the circuit breaker contact assembly. However, while the notch cut-out accommodates movement of the movable contact arm, it undesirably reduces the strength of the cradle stop pin. It is also much more difficult and costly to manufacture than the conventional (i.e., un-notched) cradle stop pin.
There is, therefore, room for improvement in cradle stop assemblies for the operating mechanisms of electrical switching apparatus, such as circuit breakers.